In particular, dehumidification, in the home but more particularly in industry, represents a large and growing market. For example, it is estimated that the number of transported containers requiring the use of means for conditioning the transported products in terms of humidity is more than two hundred million per year.
A simple means of dehumidifying the air is to bring it into contact with a highly hygroscopic substance. Thus, it is known to use silica gel, clays, and magnesium or calcium chloride. In the case of calcium chloride, its conversion from anhydrous CaCl2 to its hydrated forms involves an extremely large quantity of water being absorbed, it being possible for 1 kg of calcium chloride to absorb, at equilibrium, up to 14 kg of water. This product is also economically very useful. However, it has the drawback of becoming liquid after absorbing water, raising the problem of how to confine it. For this purpose, calcium chloride is commonly placed in open trays. This solution is unacceptable, whether in an industrial environment or for household use, because of the risk of spilling calcium chloride onto the materials being conditioned if the tray is upset. This is because, on the one hand, calcium chloride hexahydrate is very viscous and difficult to clean and, on the other hand, it is highly corrosive and may therefore damage the materials being conditioned.
FR 2 819 990, in the name of the Applicant, has proposed placing the calcium chloride in an envelope permeable to gases but impermeable to liquids, for example made of a polyethylene nonwoven. However, although this solution is effective for the packaging of fragile products, such as fruit and vegetables, it is completely unsuitable for the industrial transportation of products handled with less regard. This is because if the semi-permeable envelope were to be damaged during its use, its entire contents could escape therefrom and contaminate its environment. Moreover, since the envelope is not rigid, it is more difficult to handle it. Finally, in certain positions of the envelope, the hygroscopic substance collects into a compact mass having a decreased area of contact with the air. This reduces the effectiveness of the dehumidification.
It is also known to mix anhydrous calcium chloride or calcium chloride dehydrate with clay or with an inert absorbent substance (sawdust or wood chips) so as to absorb the liquid phase resulting from the dehumidification and to prevent liquid leaks. This mixture often limits the absorptivity of the desiccating mass.